Workable cementitious compositions

ABSTRACT

A process for modifying the slump of a concrete or mortar by the addition at different times of a water-soluble poly(alkylene oxide) and a  beta -naphthalene sulphonate-formaldehyde condensate, a plasticizer or superplasticizer which is selected from lignosulphonates, melamine sulphonate formaldehyde condensates, carboxylates and selected styrene-maleic anhydride copolymers. The poly(alkylene oxide) is preferably partially replaced by a (hydroxy)alkyl cellulose. The process is advantageously used in shotcreting.

This is a continuation of application Ser. No. 08/095,125, filed Jul.20, 1993, now U.S. Pat. No. 5,494,516.

This invention relates to cementitious compositions and moreparticularly to cementitious compositions having enhanced slumpcharacteristics.

The oldest and most widely-used assessment of the workability ofcementitious compositions such concretes or mortars is the slump test,defined in ASTM C143. A frusto-conical mould of cementitious compositionis moulded on a table and the mould then removed, the slump being thedifference in height from the table between the top of the originalmound and the level to which it falls. The bigger the slump, the betterthe workability.

Achieving sufficient slump for a sufficiently long period can provedifficult under some conditions, and it can happen that a cementitiouscomposition loses slump too quickly and sets up before the compositionis in place, with unfortunate consequences. The art-recognizedplasticizers and superplasticizers cannot rectify this problem.

It has now been found that it is possible to maintain slump of acementitious composition for a considerable period by the additionthereto of certain materials. There is therefore provided, according tothe present invention, a method of achieving sustained workability of acementitious composition, comprising the addition thereto of awater-soluble poly(alkylene oxide) of molecular weight from100,000-8,000,000 and a plasticizer or superplasticizer selected fromthe group consisting of lignosulphonates, melamine sulphonateformaldehyde condensates, polycarboxylates and styrene-maleicanhydride-based copolymers (hereinafter SMA copolymers) in free acid orsalt form selected from the group consisting of

(a) those having the following types and numbers of monomer units:##STR1## in which R is an C₂₋₆ alkylene radical

R₁ is a C₁₋₂₀ alkyl-, C₆₋₉ cycloalkyl- or phenyl group,

x, y and z are numbers from 0.01 to 100

m is a number from 1 to 100 and

n is a number from 10 to 100

with the provisos, that

i) the ratio of x to (y+z) if from 1:10 to 10:1 inclusive,

ii) the ratio of z:y is from 3:1 to 100:1 and

iii) m+n=15-100

and

(b) those having the following types and numbers of monomer units:##STR2## in which M is hydrogen or the residue of a hydrophobicpolyalkylene glycol or polysiloxane,

R, R₁, m and n are as hereinabove defined,

a, b and c are numbers from 1 to 100

with the proviso that

i) the ratio of a to (b+c) if from 1:10 to 10:1 inclusive,

ii) the ratio of c:b is from 5:1 to 100:1 and

iii) m+n=15-100

The invention further provides an admixture for use in the cementitiouscomposition, comprising a mixture of a polyalkylene oxide as hereinabovedefined and a plasticizer or a superplasticizer as hereinabove defined.

The invention further provides a concrete or mortar mixture whose slumpcharacteristics have been altered by the addition thereto of apoly(alkylene oxide) and a plasticizer or superplasticizer ashereinabove defined.

It is often very important, not only that a given concrete or mortarmixture has an adequate slump when it is being transported or worked,but also that this slump be readily reduced. The best example of thisoccurs with sprayed concrete, sometimes known as "shotcrete". Here, aconcrete is required to be pumpable (a condition which requiresconsiderable slump), but when it is sprayed on to a substrate, it isrequired to become stiff very quickly (a condition which allows nearlyno slump). Them are naturally many other uses where it would be veryconvenient to change completely the slump characteristics of a concrete.However, hitherto, drastic changes of slump have only been possible byadding accelerators or otherwise influencing the reaction between theadmixture and the cement.

It has now been found that a particular embodiment of this inventionmakes it possible to change completely the slump characteristics of acementitious composition from high to low by a relatively simpleoperation without influencing the setting of the cement. The presentinvention therefore further provides a process for modifying the slumpof a cement mix, comprising the addition to the mix of a water-solublepoly(alkylene oxide) as hereinabove defined, a plasticizer orsuperplasticizer as hereinabove defined, and a β-naphthalenesulphonate-formaldehyde condensate ("BNS"), the poly(alkylene oxide) andthe BNS being added separately, one of them being added prior to end-useof the cementitious composition.

The invention further provides the use of BNS in conjunction with awater-soluble poly(alkylene oxide) as hereinabove defined with at leastone plasticizer or superplasticizer selected from lignosulphonates,melamine sulphonate-formaldehyde condensates, polycarboxylates and SMAcopolymers, as an additive to a concrete or mortar mix to reduce theslump thereof.

The invention further provides a product adapted to reduce slump in aconcrete or mortar mix, comprising poly(alkylene oxide), BNS andplasticizer or superplasticizer as hereinabove defined, together withinstructions for their use.

The poly(alkylene oxide) suitable for use in this invention may beselected from any such suitable materials known to the art. Therequirement that the material be water-soluble means that the materialmust include at least a high proportion of oxyethylene units. It ispreferable that the materials be pure poly(ethylene oxide). It is alsopreferable that the molecular weight fie in the range2,000,000-5,000,000. Typical commercial products useful in the workingof this invention may be found, for example, in the "Polyox" (trademark) range of Union Carbide Chemicals and Plastics Company, Inc.

In an especially preferred embodiment of the invention, thepoly(alkylene oxide) is partially replaced by an alkyl or hydroxyalkylcellulose.

The alkyl or hydroxyalkyl cellulose for use in this invention may be any(hydroxy)alkyl celluloses known to the art. A number of such materials,for example methyl, ethyl and hydroxyethyl celluloses, arecommercially-available materials. Hydroxyethyl cellulose is thepreferred material.

It is essential that there be used in conjunction with the poly(alkyleneoxide) at least one plasticizer or superplasticizer selected fromlignosulphonates, melamine sulphonate-formaldehyde condensates,polycarboxylates and SMA. A plasticizer or superplasticizer is amaterial which has the facility of reducing the water content of acementitious mixture considerably (sometimes by as much as 30%). Theyare described, for example, in "Concrete Admixtures Handbook" (ed.Ramachandran, Noyes 1984) or "Concrete" (Mindess & Young, Prentice-Hall1981 ), the contents of which are incorporated herein by reference.Details of art-recognized superplasticizers are given, for example inRamachandran at pp. 211-213.

Details of the SMA copolymers, which, for the purposes of thisinvention, are the preferred (super)plasticizers, are to be found inEuropean Published Application 0 306 449 and German Offenlegungsschrift(published application) 41 42 388, the contents of which areincorporated by reference.

The BNS for use in this invention is a readily-available material,widely used as a superplasticizer in the concrete industry. It is anunusual feature of this invention that the BNS does not act in thismanner in the composition of the invention. It can be used as a powderbut it is preferred that there be used an aqueous solution containingapproximately 40% of active substance in the form of the sodium salt.

The combination of BNS with poly(alkylene oxide) and, where present,(hydroxy)alkyl cellulose and plasticizers or superplasticizers, addedsequentially as hereinunder described, has the unique ability to conferon cementitious compositions long-lasting flow (high slump) followedimmediately by a rapid stiffening (low slump). Conventional plasticizersor super-plasticizers such as melamine sulphonate-formaldehydecondensates have a good plasticising effect when used alone, but this islost after a short period and slump goes from high to low.

The mode of use of the invention is that one of the poly(alkylene oxide)and BNS is mixed into the cementitious composition mix at a suitablestage ("the first addition") and the final substance is added and mixedin prior to end-use ("the final addition"). Precisely when this finaladdition is made depends very much on the nature of the mix and therequirements of the job but this can readily be ascertained by theskilled person. Thus, if the concrete is to be poured from aconventional mixer, the second substance is added and mixed in justbefore the pour. In the case of concrete or mortar spraying, the secondsubstance is injected into the spray nozzle.

The substances can be added to the concrete mix in any order, that is,the poly(alkylene oxide) and, where present, (hydroxy)alkyl cellulosemay be incorporated into the mix and the BNS added to the mix justbefore end-use, or vice versa. The former possibility is preferred. Theplasticizers or superplasticizers may be added at any time, but it ispreferred to add them at the same time as the poly(alkylene oxide),preferably mixed with the poly(alkylene oxide).

It is additionally preferred that the poly(alkylene oxide) and theplasticizer or superplasticizer be added first, with the BNS being addedlater. This has the advantage of giving the maximum slump for thelongest time.

It is a particular feature of the invention that the use of acombination of poly(alkylene oxide) (optionally with (hydroxy)alkylcellulose)+superplasticizers with BNS in the manner hereinabovedescribed gives a relatively long period of high slump followed by arapid onset of low slump. The reduction of slump at the moment of thefinal addition is so quick that for many purposes the usual addition ofan accelerator becomes superfluous. Only in the case of shotcrete wherefast strength development is necessary will a combination of BNS with anaccelerator be added to the nozzle.

The relative quantities of the substances to be used in the working ofthis invention and their relation to the quantity of cementitiouscomposition may vary over wide limits, depending largely on thecomposition of the mix, the use to which it is to be put, the method ofapplication, the desired speed with which the slump properties are tochange and the desired initial and final slumps. Other factors such asambient temperature may have an effect on the proportions needed.

With only minor experimentation the skilled person can readily determinesuitable proportions in any given case. As a general guidelinequantities of 0.001 to 0.01% by weight of poly(alkylene oxide) and 0. 1to 1.5% by weight of the BNS (calculated as active substance), based onthe weight of cement, will be used. When (hydroxy)alkyl cellulose isused, it may replace up to 50% by weight of the poly(alkylene oxide).

The ratio of poly(alkylene oxide) and where present, (hydroxy)alkylcellulose to BNS will be from 1:100 to 1:30.

The plasticizer or superplasticizer is added at a rate of 0.03 to 0.5%(calculated as active substance) by weight of the cement.

In a further preferred embodiment, the invention provides an additivefor addition to a cement mix on batching, comprising a SMA copolymer ashereinabove described and a poly(ethylene oxide) of molecular weightfrom 2,000,000 to 5,000,000 in a ratio of from 30:1 to 4:1.

It is permissible to add any of the wide range of concrete admixtures tothe mix (prior to the addition of the second substance prior to use). Anadmixture is, according to the definition in ASTM C₁₂₅

"a material other than water, aggregates and hydraulic cement that isused as an ingredient of concrete or mortar and is added to the batchimmediately before or during its mixing"

(See, for example; "Concrete" and "Concrete Admixtures Handbook", asmentioned hereinabove). Examples of such admixtures are retarders suchas sodium phosphate and, particularly preferred, phosphonic acidderivatives, especially those available under the trade mark DEQUEST asdescribed in, for example, European Published Application No. 0 324 501,the contents whereof are incorporated herein by reference.

As hereinabove indicated, the addition of accelerators will not alwaysbe necessary for rapid stiffening. In the case of shotcrete however, itis preferred to use known accelerators such as silicates (typicallysodium silicate ("water glass") and aluminates which are added inamounts of about 2-8% by weight, based on the cement weight. A furtherfeature of the invention is, therefore, the combination of BNS withsilicate and/or aluminate.

A preferred admixture in this connection is the combination of 8 partsof sodium silicate (30-45% solution), one part of the 40% aqueoussolution of BNS and one further part of water.

The invention is generally applicable to all cementitious compositions,however constituted and however used, where a long period of workabilityand/or a relatively rapid transformation from an initial high slump to afinal low slump are required. It is especially valuable in sprayingconcrete ("shotcrete"), e.g. for permanent final linings, includingfiber shotcrete, where it gives less rebound, better orientation of anyreinforcing fibers present and higher strength. It is, also applicablein sprayable thixotropic plastering mortar, in pourable repair mortar,in slipforming concrete and in road or paving concrete.

The invention is further described with reference to the followingexamples in which all parts are expressed by weight.

EXAMPLE 1

Spraying concrete for rock support (wet method) A mixture consisting of410 parts of cement, 25 parts of silica fume, 1480 parts of sand(0-8mm), 0.6% by weight (on cement) of stabilizer (phosphonic acidderivative), 2 parts of a combination of 20 parts of copolymer ofstyrene and maleic acid ester (as obtained in Example 1 of DE 4142388)with 1.5 parts of poly(ethylene oxide)-Polyox WSR 301 of UnionCarbide--1 part of lignosulphonate and water to achieve a ratio of 0.5(water/cement & silica fume) is made up and pumped in the usual mannerthrough the hose to a nozzle where an activator combination consistingof 8 parts of sodium silicate (36% aqueous solution), 1 part of anaqueous solution (40%) of β-naphthalene sulphonate-formaldehydecondensate and 1 part of water is added (3% by weight of cement).

The initial slump of 25 cm can be kept unchanged over 11/2 hours.Nevertheless, the mixture can be sprayed in the usual manner with areduced rebound and a high early strength within 2 hours.

EXAMPLE 2

Spraying fiber concrete

A mixture consisting of 450 parts of cement, 36 parts of silica fume,1400 parts of sand (-0-8mm), 8 parts of the combination mentioned inExample 1, 50 parts of 40 mm fibers and water to achieve a ratio ofwater to cement and silica fume of 0.41 (W/C+S) is made up and pumped inthe usual manner. In the nozzle 4% by weight of cement of the activatorcombination mentioned in Example 1 is added.

The use of this mixture reduced the high fiber rebound and increased thetoughness index I₃₀.

EXAMPLE 3

Repair mortar for handspraying

    ______________________________________                                        Mix design:                                                                   cement           450    parts                                                 silica fume      25     parts (densified powder)                              sand (Dmax 6 mm) 1480   parts                                                 lignosulphonate  3      parts                                                 stabilizer (phosphonic                                                                         1      part                                                  acid derivative)                                                              combination of Example 1                                                                       4      parts                                                 Water/Cement + Silica fume                                                                     0.45                                                         ______________________________________                                    

The slump of 24 cm remained unchanged, when batching was continuedduring transport. Before spraying, 2% by weight of cement is added fromthe activator combination of Example 1.

EXAMPLE 4

Spraying mortar on a bob track

    ______________________________________                                        cement           400              kg                                          silica fume      10               kg                                          sand (0-8 mm)    1670             kg                                          polymer additive 3% of cement weight (12.5                                                                      kg)                                         (polyvinyl acetate powder)                                                    polypropylene fibers                                                                           1                kg                                          18 mm steel fibers                                                                             60               kg                                          combination of Ex. 1                                                                           8                kg                                          stabilizer (phosphonic                                                                         0.6% of cement weight(2.5                                                                      kg)                                         acid derivative)                                                              Water/Cement + Silica fume                                                                     0.45                                                         ______________________________________                                    

Add in nozzle activator of Ex. 1 (4% of Cement+Silica weight).

EXAMPLE 5

Shotcrete with a slump of 21 cm is prepared by mixing

    ______________________________________                                        cement                  400    kg                                             silica fume             30     kg                                             sand (0-8 mm)           1700   kg                                             stabilizer (phosphonic  2.8    kg                                             acid derivative)                                                              combination of Ex. 1    5      kg                                             Water/Cement + Silica fume                                                                            0.5                                                   ______________________________________                                    

A 40% solution of β-naphthalene sulphonate-formaldehyde condensate isadded in the nozzle (1% of cement+silica fume weight).

The process enables spraying of thick layers on vertical substrate.

EXAMPLE 6

Plastering mortar containing

    ______________________________________                                        cement                200    kg/m.sup.3                                       sand (0-4 mm)         1800   kg/m.sup.3                                       combination of Ex. 1  2      kg/m.sup.3                                       Water/Cement          0.5                                                     ______________________________________                                    

has a good flowable consistency. When spraying, 1.5% of cement weight ofthe solution used in Example 5 is added in the spraying nozzle

EXAMPLE 7

A flowable grouting/repair mortar is made up by mixing

    ______________________________________                                        cement                  45.4   parts                                          sand                    48.7   parts                                          calcium oxide           3.2    parts                                          silica fume             2.0    parts                                          BNS* powder             0.6    parts                                          antifoam agent          0.1    parts                                          Water/Cement + Silica fume                                                                            0.5                                                   ______________________________________                                    

when spraying, 2% cement weight of a 1% solution of Polyox WSR 301 isadded in the nozzle.

*BNS is β-naphthalene sulphonate-formaldehyde condensate.

EXAMPLE 8

Example 1 is repeated, but with 0.75 parts of the polyethylene oxideused in that example being replaced by 0.75 parts of hydroxyethylcellulose.

The slump performance of the resulting composition is similar to that ofthe composition of Example 1.

We claim:
 1. A process of maintaining the slump of a cement mix,comprising adding to a cement mix 0.001 to 0.01% by weight of cement ofa water-soluble poly(alkylene oxide) of molecular weight from100,000-8,000,000 0.03 to 0.5% by weight of cement of and a plasticizeror superplasticizer selected from the group consisting oflignosulphonates, melamine sulfonate-formaldehyde condensates,carboxylates and styrene-maleic anhydride copolymers in free acid orsalt form, said styrene-maleic anhydride copolymer selected from##STR3## in which R is a C₂₋₆ alkylene radicalR₁ is a C₁₋₂₀ alkyl-, C₆₋₉cycloalkyl- or phenyl group, x, y, and z are numbers from 0.01 to 100 mis a number from 1 to 100 and n is a number from 10 to 100 with theprovisos thati) the ratio of x to (y+z) is from 1:10 and 10:1 inclusive,ii) the ratio of z:y is from 3:1 to 100:1 and iii) m+n=15-100and##STR4## in which M is hydrogen or the residue of a hydrophobicpolyalkylene glycol or polysiloxane, R, R₁, m and n are as hereinabovedefined, a, b, and c are numbers from 1 to 100 with the provisos thati)the ratio of a to (b+c) is from 1:10 to 10:1 inclusive, ii) the ratio ofc:b is from 5:1 to 100:1 and iii) m+n=15-100.
 2. A process for reducingthe slump of a cement mix comprising the steps of adding to a cement mixas a first addition, one of either a water-soluble poly(alkylene oxide)having a molecular weight of from 100,000 to 8,000,000 or aβ-naphthalene sulfonate-formaldehyde condensate;adding, as a lateraddition, the other of said water-soluble poly(alkylene oxide) orβ-naphthalene sulfonate-formaldehyde condensate just prior to end-use ofthe cement mix; and adding, prior to said later addition, at least oneplasticizer or superplasticizer selected from the group consisting oflignosulphonates, melamine sulfonate-formaldehyde condensates,carboxylates and styrene-maleic anhydride-based copolymers in free acidor salt form, said styrene-maleic anhydride-based copolymer selectedfrom ##STR5## in which R is a C₂₋₆ alkylene radical R₁ is a C₁₋₂₀alkyl-, C₆₋₉ cycloalkyl- or phenyl group, x, y, and z are numbers from0.01 to 100 m is a number from 1 to 100 and n is a number from 10 to 100with the provisos thati) the ratio of x to (y+z) is from 1:10 and 10:1inclusive, ii) the ratio of z:y is from 3:1 to 100:1 and iii)m+n=15-100and ##STR6## in which M is hydrogen or the residue of ahydrophobic polyalkylene glycol or polysiloxane, R, R₁, m and n are ashereinabove defined, a, b, and c are numbers from 1 to 100 with theprovisos thati) the ratio of a to (b+c) is from 1:10 to 10:1 inclusive,ii) the ratio of c:b is from 5:1 to 100:1 and iii) m+n=15-100,saidwater-soluble poly(alkylene oxide) being added in an amount of 0.001 to0.01% by weight of cement, said β-naphthalenesulfonate formaldehydecondensate being added in an amount of 0.1 to 1.5% by weight of cementand said plasticizer or superplasticizer being added in an amount of0.03 to 0.5% by weight of cement.
 3. A process according to claim 2wherein the water-soluble poly(alkylene oxide) is added into the cementmix as said first addition and the β-naphthalene sulphonate-formaldehydecondensate is added to the cement mix as said later addition.
 4. Aprocess according to claim 2, in which the water-soluble poly(alkyleneoxide) is partially replaced by a (hydroxy)alkyl cellulose.
 5. A processaccording to claim 2, in which the plasticizer or superplasticizer is astyrene-maleic anhydride copolymer.
 6. A process according to claim 2 inwhich the poly(alkylene oxide) is a poly(ethylene oxide) having amolecular weight of 1,000,000-5,000,000.
 7. A process according to claim2, in which the β-naphthalene sulphonate-formaldehyde condensate isadded as an aqueous solution containing 40% by weight of a sodium saltof said β-naphthalene sulphonate-formaldehyde condensate.